1. Field of the Invention
The present invention relates to a canned motor pump, more particularly to a canned motor pump having a protrusion shaped as a raindrop at each side of a rotor, in which a narrow width of the protrusion is directed toward a rotation shaft.
2. Description of the Prior Art
FIG. 7 shows a conventional canned pump motor. The canned pump motor is comprised of a motor 10, and a pump 30 assembled with the motor 10, between which a motor end cover 11 is interposed. In a rotor 13 of the motor 10, each end of the core assembly 15 is covered with respective caps 17L,17R. A pipe type can 19 is fitted on the circumference of the core assembly 15, and both open ends 21 of the can 19 are curled.
When the impeller 31 of the pump 30 starts by power of the motor 10, intake pressure below atmospheric pressure occurs at a central inlet 33 of the impeller 31. Thus, the inside of a rotor chamber 13C is below atmospheric pressure owing to the passage 39 formed around the bush 37 adjacent to a rotational shaft 35 and the cap 17L. Therefore, a difference in pressure occurs between the inside fluid of the rotor chamber and the fluid in the housing of the pump 30 exchanged from the outlet 31T of the impeller. The pressurized fluid of the pump housing is discharged through the normal discharge route of the pump housing, and simultaneously the pressurized fluid inflows to the rotor chamber 13C through the passage communicated with the inside of the rotor chamber 13C, i.e., through the gap between the rotational shaft 35 and the bush 37 and the special passage 12 provided at the motor end cover 11. The temperature of the intake fluid due to the pressure difference is relatively lower than that of the motor coil, and heat of the rotor 13 and stator 23 is reduced.
To establish the cool flow route, a gap 43 about 0.3 mm to 0.4 mm is formed between the rotor 13 and the stator 23 as shown in FIG. 7. Efficiency of the motor depends on the size of the gap; in relation with the gap X and the motor torque T the equation is T=1/X.sup.2, in which the smaller gap contributes to the motor having good efficiency. Therefore, to increase the efficiency of the motor the gap 43 between the rotor and the stator must be reduced. The canned motor pump having the above configuration is disclosed in U.S. Pat. No. 4,465,437.
In a conventional canned motor pump, when the fluid of the pump chamber having foreign material inflows to the rotor chamber through the passage communicated with the rotor chamber, there is a problem that the foreign material clogs the fluid passage. On the other hand, the foreign material of the fluid in the rotor chamber inflows to the gap, and the rotor or the stator can wear out, thereby causing a problem of shortening the life of the pump. The metallic foreign material within metal rusty water inflows to the gap, and the metallic foreign material accumulates on the ferrous rotor and stator, thus resulting in the typical problem that the rotor and the stator become stuck.
Furthermore, in the can assembled on the circumference of the rotor, since both open ends of each can are curled on the side surface of the rotor, fluid can easily permeate the rotor assembly. Particularly, the foreign material contained in the fluid is liable to be caught at the curling portion of the rotor assembly directed to the impeller, which causes another problem.